documentclass{book}
usepackage[T1]{fontenc}
usepackage{tikz,tikzpagenodes}
usepackage[most]{tcolorbox}
usetikzlibrary{calc}
usetikzlibrary{intersections, patterns}
tcbuselibrary{skins}
usepackage{lipsum}
usepackage{xcolor,etoolbox}


definecolor{lightblue}{RGB}{199,232,250}
definecolor{darkblue}{RGB}{59,134,215}

begin{document}



begin{tikzpicture}[overlay,remember picture]
    % container
    draw[fill=darkblue,draw=none] (0,0) -- ++(5cm,0) -- ++(0,1cm)
    arc (0:90:0.5) -- ++(-4.5cm,0) -- cycle;
    % Horizontal line
    draw[darkblue, line width=2pt] (0,0) -- (textwidth,0);
    % title of container
    node[scale=1.2] at (0.2cm,0.2cm)  {textcolor{white}{Environment
        Title }};
  end{tikzpicture}


end{document}

%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
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